To effectively resolve an information security problem, a quantum key distribution (QKD) technology emerges and is currently developing towards a market and becoming practical.
In a one-way QKD system, an implementation is as follows: In a transmit apparatus, a group of random numbers are encoded on a quantum state of a quantum optical signal. After being transmitted through a quantum channel, the quantum optical signal is detected by a receiver of a receive apparatus. After implementing a series of processing processes on a classical channel, such as data comparison and negotiation, the transmit apparatus and the receive apparatus finally share a secure key including a group of random numbers. In a typical QKD system, an optical fiber used for communication between a transmit apparatus and a receive apparatus carries only a quantum optical signal. This is favorable to quantum optical signal detection, because there is no impact of additional noise brought by another optical signal in this case. However, quantum communication definitely develops towards networking and globalization in the future. At present, a development process of metropolitan area networks is based on deployment of an optical fiber network. It is impossible to tear down the original optical fiber network and deploy a new quantum network. Therefore, an only way is to perform integration based on the original optical fiber network by using a wavelength division multiplexing (WDM) technology, to obtain a quantum-classical hybrid optical network. In other words, the WDM technology needs to be used to simultaneously transmit a quantum optical signal and a classical optical signal in one optical fiber.
WDM is a technology in which two types of or a plurality of types of optical carrier signals (carrying various types of information) of different wavelengths are aggregated in the transmit apparatus by using a multiplexer, and an aggregated signal is coupled to one optical fiber of an optical line for transmission. In the receive apparatus, optical carrier signals of different wavelengths are separated by using a demultiplexer, and are further processed by an optical receiver to restore the original signals.
In the prior art, there are a plurality of bands that may be used to transmit an optical carrier signal, for example, an L band, a C band, an S band, an E band, and an O band. Wavelength ranges corresponding to all bands are different from each other. A wavelength range of the L band is from 1565 nanometers (nm) to 1625 nm, a wavelength range of the C band is from 1530 nm to 1565 nm, a wavelength range of the S band is from 1460 nm to 1530 nm, a wavelength range of the E band is from 1360 nm to 1460 nm, and a wavelength range of the O band is from 1260 nm to 1360 nm.
A solution that implements hybrid transmission of a classical optical signal and a quantum optical signal in a same optical fiber is to respectively transmit a classical optical signal and a quantum optical signal in the C band and the L band based on the WDM technology. However, in the optical fiber, Raman noise is generated after inelastic scattering occurs between a pump photon and an optical phonon, and a wavelength of a generated scattered photon is less than or greater than that of pump light, and is corresponding to an anti-Strokes scattering region or a Stokes scattering region. In addition, a scattering intensity of the Stokes scattering region is greater than that of the anti-Strokes scattering region. Therefore, when the quantum optical signal is configured to be in the L band corresponding to a relatively large wavelength, the quantum optical signal is mainly affected by the Stokes scattering region. In this case, the quantum optical signal is greatly affected by the Raman noise.
In conclusion, a quantum communication method and a related apparatus are urgently required, to reduce impact of the Raman noise on the quantum optical signal when hybrid transmission of the classical optical signal and the quantum optical signal is performed by using one optical fiber.